Impacts Of Land Use Changes On Water Balance In The Ruvu River Sub-Basin: The Case On Mvuha River Sub-Catchment

ABSTRACT

This study was carried out to assess spatial and temporal land use changes that have occurred over a period of 40 years in Mvuha River sub-catchment and its impacts to the water balance. The specific objectives of this study were i) to determine the spatial and temporal changes on land use and land cover in Mvuha River sub-catchment for the past forty years, ii) carry out statistical and trend analysis of temporal rainfall and river discharge and iii) to determine runoff hydrologic response and water quality response to land use in the sub-catchment. Land use and land cover change detection was conducted using Remote sensing and GIS techniques, trend analysis of temporal rainfall and river discharge was evaluated using statistical methods and lastly rainfall simulation experiments were used to determine runoff, hydrologic and water quality response to land use. Results showed that there were significant land use changes and/or conversions. For example forest, bushland and swamps decreased while woodland, grassland, settlement and agriculture increased. Analysis of temporal rainfall data showed that rainfall trend is almost constant and analysis of river discharge data showed a decreasing discharge rate. Correlation of longterm rainfall data and discharge rate showed a weak positive correlation which imply weak association. Rainfall simulation experiments revealed significant difference on runoff, hydrologic response and water quality response with land use. Grazing showed the highest runoff rate followed by cultivation and lastly forested land use. In terms of water quality, grazing lands had the highest insoluble suspended solids followed by agricultural land use and lastly forested land use which had the least insoluble suspended solids. The study recommends that Wamii-Ruvu water Basin office (WRBO) to have clear strategies to protect forests from encroachers and reduced livestock grazing activities in the catchment. In addition, suitable land use planning and management strategies are needed in order to avoid catchment degradation